font chooser dialog: Improve sensitivity handling

We should not tie the sensitivity of the select button
to the tweak action, since there may be fonts which are
selectable, but not tweakable.

Instead, enable the select button when a font is selected,
as it should be.

gtk/gtkfontchooserdialog.c

@@ -208,6 +208,21 @@ gtk_font_chooser_dialog_class_init (GtkFontChooserDialogClass *klass)
   gtk_widget_class_bind_template_callback (widget_class, font_activated_cb);
 }
 
+static void
+update_button (GtkFontChooserDialog *dialog)
+{
+  GtkFontChooserDialogPrivate *priv = dialog->priv;
+  PangoFontDescription *desc;
+
+  desc = gtk_font_chooser_get_font_desc (GTK_FONT_CHOOSER (priv->fontchooser));
+
+  gtk_widget_set_sensitive (priv->select_button, desc != NULL);
+
+  if (desc)
+    pango_font_description_free (desc);
+}
+
+
 static void
 gtk_font_chooser_dialog_init (GtkFontChooserDialog *fontchooserdiag)
 {
@@ -222,11 +237,9 @@ gtk_font_chooser_dialog_init (GtkFontChooserDialog *fontchooserdiag)
   _gtk_font_chooser_set_delegate (GTK_FONT_CHOOSER (fontchooserdiag),
                                   GTK_FONT_CHOOSER (priv->fontchooser));
 
-  g_object_bind_property (gtk_font_chooser_widget_get_tweak_action (priv->fontchooser),
-                          "enabled",
-                          priv->select_button,
-                          "sensitive",
-                          G_BINDING_SYNC_CREATE);
+  g_signal_connect_swapped (priv->fontchooser, "notify::font-desc",
+                            G_CALLBACK (update_button), fontchooserdiag);
+  update_button (fontchooserdiag);
 }
 
 /**